ENGINE VIBRATION

Types of Harmonic Balancers

The harmonic balancer is the most misunderstood engine part.  The confusion comes from its name.  Engine harmonics is a general term to lump various vibrations together.  Balancer, or to balance a rotating assembly, is a common engine performance service.  So a harmonic balancer must be a simple, one part fix, to smooth out an engine.  Not always true.

The harmonic balancer reduces torsional vibration.  To reduce means to damp.  More accurate, a harmonic balancer is a torsional vibration damper (TVD) -  as in Vibratech TVD, original inventor of the viscous torsional damper and Fluidampr brand.

The terms damper, dampener and harmonic balancer are all interchangeable.  Chances are you’ll find the term damper used by performance parts retailers and professional race engine builders.  The term, harmonic balancer, is common among OE replacement part stores.

There are many harmonic balancer options.  Common to all are a few basic design principles you need to know before choosing one.

 

Internal balance vs external balance

Internal combustion engines come in all sorts of configurations.  None is more important than knowing if it is internal balance or external balance.  

If there is not enough space within the engine block to place all of the necessary crankshaft counterweights, then designers will add that weight to the harmonic balancer and / or flywheel.  Since this weight is outside the engine block it is referred to as external balance.

Today, the Ford Power Stroke and GM Duramax are two popular external balance engines.  Both are large displacement light duty truck diesels.  Classic external balance engines include the:

• Ford Windsor, Cleveland & FE engines
• Chevy 400ci Small Block
• Chevy 454-502ci Big Blocks
• Oldsmobile V8s

External balance harmonic balanncer
External balance.  Note the large counterweight mass CNC machined into the housing.  Fluidampr #800221 for 6.7L Ford Power Stroke applications.

 

Be aware that external to internal balance conversion is a popular performance upgrade.  Internal balance dampers are available from Fluidampr and other brands for this conversion.  When working on any vehicle, especially classic muscle cars, it is best practice to physically verify an internal or external balance set up.  You can cause spectacular devastation with unbalanced rotating assembly weight otherwise.

External balance harmonic balancer with removable hub
Fluidampr for 454-502ci external balance Chevy Big Block.  The removable hub contains the counterweight mass.  By changing only the hub this damper can then be used on an internal balance conversion.

Internal balance refers to all the necessary crankshaft counterweights being within the engine block.  There is no counterweight mass on the harmonic balancer.  Most modern automotive engines are internal balance.

Internal balance harmonic balancer
Internal balance.  Fluidampr #571101 for Subaru FA20 engines.



Broad range vs narrow range

Torsional vibration occurs throughout the RPM range.  Some RPMs see higher vibration amplitudes than others.  Some uncomfortable vibration may be at cruising RPM.  In a stock passenger car or truck it makes sense to target torsional vibration control at that specific RPM.  A tuned narrow range harmonic balancer is a cost effective option for OE designers.

OEM tuned narrow range harmonic balancer
OEM harmonic balancer with frequency range stamp.  It controls torsional vibration in a narrow range between 380 to 420 hertz.

What happens if you modify the rotating assembly and that target shifts?  Your stock tuned narrow range harmonic balancer is no longer optimal.  Broad range harmonic balancers, like premium ones found in professional motorsports and high-end factory sports cars, provide durability and performance across the entire RPM range.

Fluidampr performance dampers are broad range.